CN113676031A - Drive system with common DC bus - Google Patents

Abstract

The invention discloses a system, comprising: a pre-charge circuit configured to generate Direct Current (DC) electrical power; a common DC bus; and a plurality of inverters, each inverter including: a local DC bus; a capacitor network connected to a local DC bus; an electrical network connected to the local DC bus, the electrical network configured to generate an Alternating Current (AC) drive signal; and a plurality of switching assemblies, each switching assembly associated with one of the inverters and configured to control whether a local DC bus and a capacitor network of the associated inverter are electrically connected to the common DC bus or to the pre-charge circuit.

Description

Drive system with common DC bus

Cross Reference to Related Applications

This application claims benefit of U.S. provisional application No. 63/024,610 entitled "DRIVE SYSTEM WITH COMMON DC BUS" filed on 14/5/2020, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to a fault tolerant drive system with a common Direct Current (DC) bus.

Background

The drive system may be used to drive a load, such as a motor. Some drive systems include a common DC bus that can supply DC power to more than one inverter.

Disclosure of Invention

In one aspect, a system comprises: a pre-charge circuit configured to generate Direct Current (DC) electrical power; a common DC bus; and a plurality of inverters, each inverter including: a local DC bus; a capacitor network connected to the local DC bus; an electrical network connected to the local DC bus, the electrical network configured to generate an Alternating Current (AC) drive signal; and a plurality of switching assemblies, each switching assembly associated with one of the inverters and configured to control whether a local DC bus and a capacitor network of the associated inverter are electrically connected to the common DC bus or to the pre-charge circuit.

Implementations may include one or more of the following features. The pre-charge circuit may be configured to provide DC electrical power to the capacitor network of the local DC bus of at least one other of the plurality of inverters when the local DC bus of at least one of the plurality of inverters is electrically connected to the common DC bus.

The pre-charge circuit may be electrically connected to an AC power source, and the pre-charge circuit may further include at least one electronic component configured to convert AC electrical power to DC electrical power. The at least one electronic component configured to convert AC electrical power to DC electrical power may be a diode.

In some embodiments, the system further comprises a converter electrically connected to the AC power source and the common DC bus, wherein the converter is configured to convert AC electrical power from the AC power source to DC electrical power and to provide the DC electrical power to the common DC bus. The converter may be a front end rectifier and the AC power source may be a multi-phase high voltage electrical power distribution network.

In some embodiments, the pre-charge circuit is electrically connected to the common DC bus and the pre-charge circuit receives DC electrical power from the common DC bus.

The system may also include a control system configured to control the plurality of switch assemblies.

The pre-charge circuit may be a secondary pre-charge circuit, and in these embodiments, the system may additionally include a common pre-charge circuit electrically connected to the common DC bus, wherein the common pre-charge circuit is configured to provide a DC pre-charge current to all of the capacitor networks when the capacitor networks are electrically connected to the common DC bus, and the secondary pre-charge circuit is configured to pre-charge a capacitor network associated with another inverter when at least some of the other capacitor networks are electrically connected to the common DC bus.

In another aspect, a method comprises: electrically connecting a local DC bus of a first inverter to the common DC bus, wherein the first inverter is associated with a first switching assembly; operating a second switching assembly associated with the second inverter to electrically connect the local DC bus of the second inverter to the pre-charge circuit when the local DC bus of the first inverter is electrically connected to the common DC bus and when the local DC bus of the first inverter receives DC electrical power from the common DC bus; comparing a voltage of a capacitor network electrically connected to a local DC bus of a second inverter to a threshold voltage when the local DC bus of the first inverter is electrically connected to the common DC bus and when the local DC bus of the first inverter receives DC electrical power from the common DC bus; and determining whether to disconnect the local DC bus of the second inverter from the pre-charge circuit and whether to connect the local DC bus of the second inverter to the common DC bus based on the comparison. The first switching assembly is configured to connect the local DC bus of the first inverter to the common DC bus or the pre-charge circuit, and the second switching assembly is configured to connect the local DC bus of the second inverter to the common DC bus or the pre-charge circuit.

Implementations may include one or more of the following features.

Determining whether to disconnect the local DC bus of the second inverter from the pre-charge circuit and whether to connect the local DC bus of the second inverter to the common DC bus based on the comparison may include disconnecting the first inverter from the pre-charge circuit if a measured voltage of the local DC bus of the second inverter is equal to or greater than a threshold voltage.

The method may further include precharging the capacitor network of the first inverter with a common precharge circuit electrically connected to the common DC bus prior to operating the second switching component.

In another aspect, a system comprises: a pre-charge circuit configured to generate Direct Current (DC) electrical power; a common DC bus; a plurality of inverters, each inverter comprising: the system includes a local DC bus, a capacitor network electrically connected to the local DC bus, and an electrical network electrically connected to the local DC bus, the electrical network configured to generate an Alternating Current (AC) drive signal. The capacitor network of each inverter is configured to be electrically connected to a common DC bus or precharge circuit.

Implementations of any of the techniques described herein may include apparatuses, devices, systems, and/or methods. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

Drawings

Fig. 1A shows an example of a drive system.

FIG. 1B illustrates an example of an inverter that may be used in the drive system of FIG. 1A.

Fig. 1C shows an example of an electronic network that may be used in the inverter of fig. 1B.

Fig. 2A, 3, 4, 5C-5E, and 6 illustrate various other example embodiments of drive systems.

Fig. 2B shows an example of a converter.

Fig. 2C shows another example of an inverter.

Fig. 2D shows an example of a switch assembly.

Fig. 5A and 5B illustrate example data.

Fig. 7-9 are flowcharts of various example processes.

Detailed Description

Referring to fig. 1A, a block diagram of an example of a drive system 100 is shown. Drive system 100 includes inverters 140_1 through 140_ N (collectively referred to as N inverters 140), where N is an integer greater than one. Each of the N inverters is connected to a respective load 102_1 to 102_ N. For example, the loads 102_1 to 102_ N may be electric motors 102_1 to 102_ N, which may be brushless DC motors, permanent magnet AC motors, or AC induction motors, etc. The motors 102_1 to 102_ N may be used in, for example, a warehouse, distribution center, or manufacturing facility, and may be part of a heating, ventilation, and air conditioning (HVAC) system; a material handling system; or a pump system. When N inverters 140 are operational, each of these inverters is capable of generating a respective drive signal 104_1 to 104_ N, which is provided to a respective load 102_1 to 102_ N. The drive signals 104_1 to 104_ N are three-phase AC electrical signals (e.g., three-phase voltage and current signals).

Fig. 1B is a block diagram of the inverter 140_ 1. Inverter 140_1 includes an electronic network 148_1 and a capacitor network 147_ 1. The inverter 140_1 output is connected to the load 102_ 1. The input of inverter 140_1 includes a local DC bus 142_1 having a high side DC + and a low side DC-. The capacitor network 147_1 is connected across the local DC bus 142_ 1. In other words, capacitor network 147_1 is connected to high side DC + and low side DC-. FIG. 1C is a block diagram of electronic network 148_ 1. Electronic network 148_1 includes controllable switching elements SW 1-SW 6, such as Insulated Gate Bipolar Transistors (IGBTs). The switches SW 1-SW 6 are arranged to form an H-bridge.

The other N inverters 140 are configured in the same manner. In other words, inverters 140_1 to 140_ N each include a respective local DC bus 142_1 to 142_ N, a respective capacitor network 147_1 to 147_ N, and a respective electronic network 148_1 to 148_ N configured as shown in fig. 1B and 1C.

In a typical situation, all local DC buses 142_1 to 142_ N are connected to common DC bus 110, and N inverters 140 are powered by common DC bus 110. However, in some conditions, one or more of the inverters 140 may be disconnected from the drive system 100, e.g., for maintenance or replacement, and then reconnected to the system 100, or an operator of the drive system 100 determines that additional inverters 140 should be added to the drive system 100. The precharge circuit 130 allows the capacitor networks of such individual inverters to be precharged prior to connection to the common DC bus 110 without interrupting the operation of any of the inverters already connected to the DC bus 110.

For purposes of providing an example of such a situation, inverter 140_1 is powered down and disconnected from common DC bus 110 for repair. All other N inverters 140 remain operational, remain connected to DC bus 110, and continue to receive electrical power from common DC bus 110. When repair of inverter 140_1 is complete, an operator of drive system 100 wishes to reconnect inverter 140_1 to common DC bus 110. When inverter 140_1 is in an off state (e.g., not connected to common DC bus 110), the voltage across capacitor 147_1 is zero. However, the voltage across common DC bus 110 is not zero because common DC bus 110 continues to provide power to the other N inverters 140. If inverter 140_1 were to be connected to common DC bus 110 immediately after being in the off state, a rush current may occur in capacitor network 147_ 1. Such surge currents can be destructive, so it is desirable to avoid them forming or to reduce the amount of surge current that occurs.

The pre-charge circuit 130 is used to boost or increase the voltage of the capacitor network 147_1 prior to connecting the local DC bus 142_1 to the common DC bus 110 so that inrush currents that may otherwise occur in the capacitor network 147_1 are reduced or eliminated. Continuing with the above example, to bring inverter 140_1 back into service, inverter 140_1 is first connected to precharge circuit 130 and not to common DC bus 110. The local DC bus 142_1 receives electrical power from the pre-charge circuit 130 and the voltage across the capacitor network 147_1 is boosted or increased. When the voltage across capacitor network 147_1 is the same as or differs from the voltage across common DC bus 110 by less than a threshold amount, local DC bus 142_1 is disconnected from pre-charge circuit 130 and connected to common DC bus 130. Inverter 142_1 may then operate and may generate drive signal 104_ 1.

By first connecting the local DC bus 142_1 to the pre-charge circuit 130, and allowing the voltage across the capacitor 147_1 to gradually rise before connecting the local DC bus 142_1 to the common DC bus 110, inrush currents that might otherwise occur in the capacitor 147_1 are reduced or eliminated. Furthermore, when inverter 142_1 is connected to precharge circuit 130, all other N inverters 140 remain connected to common DC bus 110. Thus, there is no service interruption for the other N inverters 140, and drive system 100 operates in a fault tolerant manner.

Some existing motor drive systems employ a common DC bus, but also include a pre-charge circuit for the local DC bus of each inverter. On the other hand, drive system 100 does not include an instance of a precharge circuit 130 for each local DC bus 142_1 to 142_ N of a respective inverter 140_1 to 140_ N, and each local DC bus 142_1 to 142_ N of the N inverters 140 does not have its own dedicated precharge circuit. Conversely, the precharge circuit 130 may be electrically connected to any of the local DC buses 142_1 to 142_ N.

By using a single precharge circuit 130 for more than one of the local DC buses 142_1 through 142_ N, the drive system 100 is simpler and less expensive than a design that uses dedicated precharge circuits for the local DC buses of each inverter. For example, drive system 100 has simpler wiring and fewer components than a drive system having dedicated pre-charge circuits for the local DC bus of each inverter. Furthermore, even if the drive system 100 includes a single precharge circuit 130, the drive system 100 can still operate in a fault tolerant manner. Further, the configuration of drive system 100 allows one or more of the N inverters 140 to be disconnected from common DC bus 110 while the other ones of the N inverters 140 remain connected to common DC bus 110.

Fig. 2A, 3, 4, 5C-5E, and 6 are schematic diagrams of various embodiments of drive systems including precharge circuits such as precharge circuit 130. Fig. 7-9 show various examples of processes for operating such drive systems.

Fig. 2A is a schematic diagram of a drive system 200. The driving system 200 includes inverters 240_1 to 240_ N, where N is an integer greater than one. The inverters 240_1 to 240_ N are collectively referred to as N inverters 240. Each inverter 240_1 to 240_ N has a respective local DC bus 242_1 to 242_ N, a respective electronic network 248_1 to 248_ N, and a respective capacitor network 247_1 to 247_ N. Each of the capacitor networks 247_1 to 247_ N is connected across a respective local DC bus 242_1 to 242_ N. The drive system 200 also includes a precharge circuit 230 that includes output nodes 230a and 230 b. The precharge circuit 230 provides a DC output current at output nodes 230a and 230 b. Prior to connecting the local DC buses to common DC bus 210, the DC output current is used to boost or increase the voltage of any of local DC buses 242_1 through 242 — N, as discussed in more detail below. The pre-charge circuit 230 may include any type of electronic components arranged in any configuration that results in a DC output. Examples of various precharge circuits are shown with respect to fig. 3, 4, and 6.

Referring also to fig. 2B, the common DC bus 210 receives DC power from the converter 220. Converter 220 receives three-phase AC electrical power from AC power source 201. AC power source 201 may be, for example, a high voltage distribution system, such as an AC power grid that distributes AC electrical power having a fundamental frequency of, for example, 50 hertz (Hz) or 60Hz and has an operating voltage of up to 690V. In another example, the AC power source 201 may be a generator. In the example of fig. 2B, AC power supply 201 has three phases referred to as A, B and C. Common DC bus 210 includes a high side 210a and a low side 210 b. The potential difference between the high side 210a and the low side 210b is referred to as the bus voltage (V _ bus).

Converter 220 is any type of electrical network capable of converting AC electrical power to DC electrical power. In the example of fig. 2B, converter 220 is a three-phase six-pulse bridge front-end rectifier including diodes D1 through D6. Each diode D1-D6 includes a cathode and an anode and is associated with a forward bias voltage. Each diode D1-D6 allows current to flow in the forward direction (from anode to cathode) when the voltage of the anode is greater than the voltage of the cathode by at least a bias voltage. When the voltage difference between the anode and the cathode is less than the forward bias voltage, the diode does not conduct current in the forward direction. Phase a of AC source 201 is electrically connected to the anode of diode D1 and the cathode of diode D4. Phase B of the AC source 201 is electrically connected to the anode of the diode D3 and the cathode of the diode D6. The C phase of the AC source 201 is electrically connected to the anode of the diode D5 and the cathode of the diode D2. Diodes D1-D6 rectify the input current from the respective phase into a DC current id flowing on common DC bus 210. Other embodiments are also possible. For example, the converter 220 may be an active front-end rectifier or various single-phase rectifier front-end circuits.

Referring also to fig. 2C, an example configuration of inverter 240_1 is shown. The same configuration may be used for the other N inverters 240. The inverter 240_1 includes a network 248_1 of electronic switches SW1 through SW6 connected across the local DC bus 242_ 1. The local DC bus 242_1 has a high side DC + and a low side DC-. The inverter 240_1 also includes a capacitor network 247_1 connected across the local DC bus 242. In other words, capacitor network 247_1 is connected to the high side DC + and the low side DC-. Capacitor network 247_1 includes one or more capacitors.

Each electronic switch SW 1-SW 6 may be, for example, an Insulated Gate Bipolar Transistor (IGBT) and/or another type of controllable switch. The electronic switches SW 1-SW 6 are arranged to cause the inverter 240_1 to generate the AC drive signal 204_1 from the DC power provided to the local DC bus 242_ 1. For example, local DC bus 242_1 may receive DC power from common DC bus 210. Inverter 240_1 modulates the DC power to a three-phase AC drive signal 204_ 1. The three-phase AC drive signal 204_1 has phase components 204u, 204v, 204 w. Each phase 204u, 204v, and 204w is a series of voltage pulses having an amplitude sufficient to operate the load 202_ 1. The switching frequency of the three-phase AC drive signal 204_1 may vary between, for example, 1kHz and 20kHz, with the upper limit of the frequency determined by the limits of the switching speed of the electronic components SW1 to SW6 and the system thermal and performance requirements.

The inverter 240_1 may implement, for example, a Pulse Width Modulation (PWM) technique to modulate the DC power on the local DC bus 242_1 into the three-phase AC drive signal 204_ 1. The PWM technique may be implemented based on any type of control algorithm, such as 6-step electronic commutation, various field-oriented controls, space vector PWM, or sinusoidal PWM. The PWM technique may be implemented by the control system 245 or by the control system 250 (fig. 2A). In the example shown, the control system 245 generates gating signals 246 (which consist of 6 gate signals, one for each switch) that control the switching of the electronic switches SW 1-SW 6. The gating signal 246 controls the switching of the electronic switches SW1 through SW6 such that the DC power at the local DC bus 242_1 is modulated into the drive signal 204_ 1. The amplitude, frequency, and phase of the drive signal 204_1 determine the operating characteristics of the load 202_1 (e.g., motor) such that providing the drive signal 204_1 to the motor 202_1 causes the motor 202_1 to operate at a particular torque and/or speed and/or in a particular direction. In other examples, the control system 250 generates the gating signal 245.

Referring again to fig. 2A, each inverter 240_1 through 240_ N is associated with a respective switch assembly 270_1 through 270_ N, as described below. Fig. 2D is a block diagram of the switch assembly 270_ 1. The switch assembly 270_1 includes two switch components 243_1 and 244_ 1. The switching components 243_1 and 244_1 may be implemented with various devices, such as, for example, a contactor, a relay, or a transistor. Each of the switching components 243_1 and 244_1 includes terminals 1, 2, 3. The high side DC + of the local DC bus 242_1 is electrically connected to terminal 1 of the switching component 243_ 1. Terminal 2 of switching component 243_1 is electrically connected to high side 210a of common DC bus 210. Terminal 3 of the switching section 243_1 is electrically connected to the output terminal 230a of the precharge circuit 230. The low side DC-of the local DC bus 242_1 is electrically connected to terminal 1 of the switch component 244_ 1. Terminal 2 of switching component 244_1 is electrically connected to the low side 210b of the common DC bus 210. Terminal 3 of switching element 244_1 is electrically connected to output node 230b of precharge circuit 230.

When terminal 1 of switch component 243_1 is electrically connected to terminal 2 of switch component 243_1 and terminal 1 of switch component 244_1 is electrically connected to terminal 2 of switch component 244_1, local DC bus 242_1 is electrically connected to common DC bus 210. When terminal 1 of switch component 243_1 is electrically connected to terminal 3 of switch component 243_1 and terminal 1 of switch component 244_1 is electrically connected to terminal 3 of switch component 244_1, local DC bus 242_1 is electrically connected to precharge circuit 230.

The state of the switching components 243_1 and 244_1 is controlled by the control system 250. Control system 250 generates control signal 251 that is provided to switch components 243_1 and 244_1 to cause the components to change state. The other N switch assemblies 270 also include two switch components and are also configured and arranged in the manner shown in fig. 2D.

Control system 250 includes an electronic processing module 252, an electronic storage device 254, and an input/output (I/O) interface 256. The electronic processing module 252 includes one or more electronic processors. The electronic processor of module 252 may be any type of electronic processor and may or may not include a general purpose Central Processing Unit (CPU), a Graphics Processing Unit (GPU), a microcontroller, a Field Programmable Gate Array (FPGA), a Complex Programmable Logic Device (CPLD), and/or an Application Specific Integrated Circuit (ASIC).

Electronic storage 254 may be any type of electronic memory capable of storing data and instructions in the form of computer programs or software, and electronic storage 254 may include volatile and/or non-volatile components. Electronic storage 254 and processing module 252 are coupled such that processing module 252 can access or read data from electronic storage 254 and write data to the electronic storage.

Electronic storage 254 stores instructions that, when executed, cause electronic processing module 252 to analyze data and/or retrieve information. For example, the electronic storage 254 may store informational instructions that, when executed, compare a measured value of the inverter's local DC bus to an expected or measured value of V _ bus. The electronic storage 254 may also store instructions for implementing PWM control or other control techniques of the inverters 240_ 1-240 _2, for example, in the form of a computer program. For example, electronic storage 254 may store instructions that, when executed, generate gating signal 264. Electronic storage 254 may store instructions implementing the processes described in fig. 7-9, for example, in the form of computer programs, functions, or subroutines.

Electronic storage 254 may also store information about system 200. The electronic storage 254 may also store information regarding typical or expected ranges of various characteristics (e.g., amplitude, frequency, and/or phase) of the drive signals 204_1 through 204_ N during normal operation.

The I/O interface 256 may be any interface that allows a human operator and/or an autonomous process to interact with the control system 250. I/O interface 256 may include, for example, a display such as a Liquid Crystal Display (LCD), a keyboard, audio inputs and/or outputs such as speakers and/or microphones, visual outputs such as lights, Light Emitting Diodes (LEDs) in addition to or in place of a display, serial or parallel ports, Universal Serial Bus (USB) connections, and/or any type of network interface such as, for example, an ethernet. The I/O interface 256 may also allow contactless communication over, for example, an IEEE 802.11, bluetooth, or Near Field Communication (NFC) connection. The control system 250 may operate, configure, modify, or update, for example, through the I/O interface 256.

I/O interface 256 can also allow system 200 to communicate with systems external to and remote from system 200. For example, the I/O interface 256 may comprise a communication interface that allows communication between the control system 250 and a remote station (not shown) or between the control system 250 and a separate monitoring device. The remote station or monitoring device may be any type of station through which an operator can communicate with the control system 250 without making physical contact with the control system 250. For example, the remote station may be a computer-based workstation, a smartphone, a tablet, or a laptop computer connected to the motor control system 250 via a service protocol, or a remote control connected to the control system 250 via radio frequency signals.

FIG. 3 is a schematic diagram of another example drive system 300. The drive system 300 includes a converter 320, a precharge circuit 330, and N inverters 240. In the example of fig. 3, N is two, and inverters 240_1 and 240_2 are shown. The drive system 300 may include more than two inverters. Converter 320 receives a three-phase AC input and produces a DC output at common DC bus 310. The converter 320 may be configured as shown in fig. 2B or in any other manner known in the art.

The common DC bus 310 includes a high side 310a and a low side 310 b. The potential difference between the high side 310a and the low side 310b is the voltage across the common DC bus 310 or the common DC bus 310 voltage and is referred to as V _ bus. The current flowing on the common DC bus 310 is id. Common DC bus 310 may be electrically connected to any or all of N inverters 240.

The precharge circuit 330 includes input nodes 331A, 331B, 331C and an output node 332. Precharge circuit 330 is configured to provide DC current (labeled i _330) to any inverter connected to output node 332 before that inverter is connected to common DC bus 310. The precharge circuit 330 reduces or eliminates inrush current that may otherwise occur in the capacitor network 247_1 or 247_ 2.

Each input node 331A, 331B, 331C is electrically connected to one of the phases of the AC source. Thus, the precharge circuit 330 receives an AC input. In the example shown, input node 331A is electrically connected to phase a, input node 331B is electrically connected to phase B, and input node 331C is electrically connected to phase C.

The precharge circuit 330 includes rectifying elements 333A, 333B, and 333C and an impedance 334. Each rectifying element 333A, 333B, 333C is any element capable of converting AC electrical power to DC electrical power. In the example shown, each rectifying element 333A, 333B, 333C is a diode electrically connected anode to one phase of the AC source and cathode to the impedance 334. Impedance 334 is used to reduce the magnitude of the current flowing from output node 332.

In the example of fig. 3, the impedance 334 is a resistor. However, other electronic components capable of reducing the current flowing from the output node 332 may be used. Further, although the rectifying elements 333A, 333B, 333C and the impedance 334 are shown as each comprising a single element, any of the rectifying elements 333A, 333B, 333C and/or the impedance 334 may comprise more than one element and may be a network of connected electrical elements. Furthermore, embodiments other than the one shown in fig. 3 are also possible. For example, precharge circuit 330 may be connected to less than all of phases A, B and C. Precharge circuit 330 may be connected to any two of phases A, B, C or any one of phases A, B, C.

The drive system 300 further comprises switching means 343_1, 343_2, 344_1 and 344_ 2. Each of the switching devices 343_1, 343_2, 344_1, and 344_2 has an open state and a closed state. The state of switching devices 343_1, 343_2, 344_1, and 344_2 can be controlled with a controller, such as control system 250 (fig. 2A). Each switching device 343_1, 343_2 controls the electrical connection between the respective inverter 240_1, 240_2 and the common DC bus 310. Each switching device 344_1, 344_2 controls the electrical connection between the respective inverter 240_1, 240_2 and the precharge circuit 330.

Each of the switching devices 343_1, 343_2, 344_1, and 344_2 comprises a switch or a switching component. For example, the switching device 343_1 includes switches 343a _1 and 343b _ 1. When the switches 343a _1 and 343b _1 are closed, the switching device 343_1 is in a closed state, and the inverter 240_1 is electrically connected to the common DC bus 310. When the switches 343a _1 and 343b _1 are open, the switching device 343_1 is in an open state and the inverter 240_1 is electrically disconnected from the common DC bus 310.

Switching device 344_1 includes switches 344a _1 and 344b _ 1. When the switches 344a _1 and 344b _1 are closed, the switching device 344_1 is in a closed state, and the inverter 240_1 is electrically connected to the precharge circuit 330. When the switches 344a _1 and 344b _1 are open, the switching device 344_1 is in an open state and the inverter 240_1 is electrically disconnected from the precharge circuit 330. The switching devices 343_2 and 344_2 include respective switches 343a _2, 343b _2 and 344a _2, 344b _2 that are configured to connect the inverter 240_2 to the common DC bus 310 or the precharge circuit 330 in the same manner.

The drive system 300 also includes sensors 349_1 and 349_ 2. In the example of FIG. 3, sensors 349_1 and 349_2 are voltage sensors. Sensor 349_1 measures the potential difference between common DC bus 310 and local DC bus 242_ 1. Sensor 349_2 measures the potential difference between common DC bus 310 and local DC bus 242_ 2.

FIG. 4 is a schematic diagram of another example drive system 400. Drive system 400 is the same as drive system 300 (fig. 3), except that drive system 400 further includes a common precharge switch 480. The common precharge switch 480 is connected to the high side 310a of the common DC bus 310. The common precharge switch 480 includes a resistive element 482. When common precharge switch 480 is in a first state (such as shown in fig. 4), current 410i flows through resistive element 482 to any inverter connected to common DC bus 410. In the second state, resistive element 482 is bypassed and current 410i does not flow through resistive element 482.

Fig. 5A and 5B show example data of the drive system 500 (fig. 5C to 5E). Drive system 500 is the same as drive system 400 (FIG. 4), except that drive system 500 includes three inverters 240_1, 240_2, and 240_ 3. The data shown in fig. 5A and 5B relate to a scenario in which a third inverter 240_3 is added to the drive system 500 when the inverters 240_1 and 240_2 are turned on. Fig. 5A shows the current as a function of time. Fig. 5B shows voltage as a function of time. Fig. 5A and 5B start at time 0 and include two time periods: time period t1 and time period t2 occurring after time period t 1. The x-axis (time axis) is the same in fig. 5A and 5B. Fig. 5C shows the drive system 500 during a time period t 1. Fig. 5D shows the drive system 500 during a time period t 2. Fig. 5E shows the drive system 500 immediately after the time period t 2.

Immediately before time period t1, drive system 500 is in an off state (e.g., when converter 320 is disconnected from the AC source), and the voltage of each of capacitor networks 247_1 and 247_2 is zero. At time 0, time period t1 begins. Fig. 5C shows the system 500 during a time period t 1. Inverters 240_1 and 240_2 are connected to common DC bus 310, and common precharge switch 480 is in a first state. Capacitor networks 247_1 and 247_2 are precharged with current 410i flowing through resistive element 482. The voltage of the capacitor networks 247_1 and 247_2 increases from 0 to a voltage V1, as shown in the graph labeled 547 in fig. 5B. Voltage V1 is a predetermined threshold voltage that is equal to or close to the expected steady state value of V _ bus. When the voltage of each of the capacitor networks 247_1 and 247_2 reaches V1, the precharge circuit 480 transitions to a second state such that current 410i flows in the DC common bus 310 and to the capacitor networks 247_1 and 247_2 and not in the resistive element 482. The voltage of the capacitor networks 247_1 and 247_2 rises to V _ bus. The time period t1 ends, and the time period t2 may begin.

The time period t2 is shown on fig. 5A and 5B as occurring immediately after the time period t 1. However, this is not necessarily the case. At the end of time period t1, inverters 240_1 and 240_2 may operate and may continue to operate for any amount of time until inverter 240_3 is added to drive system 500. Thus, in actual operation, there may be a period of time between the end of time period t1 and the beginning of time period t2, and then time period t2 begins, only when an additional inverter (in this example, inverter 240_3) is ready to be connected to the common DC bus.

The current flowing to the third inverter 240_3 during time period t1 is shown in the graph labeled i _330 in fig. 5A. The voltage across the capacitor network 247_3 is shown in the graph labeled 547x in fig. 5B. Third inverter 240_3 is offline and is not connected to common DC bus 310 or precharge circuit 330 during time period t 1. Therefore, during the time period t1, no current flows to the capacitor network 247_3 of the inverter 240_3, and the voltage across the capacitor network 247_3 is 0, as shown in fig. 5A and 5B.

Fig. 5D shows the system 500 during a time period t 2. The time period t2 begins when additional inverters 240_3 are added to the drive system 500. For example, the time period t2 may be initiated due to a manual indication from an operator of the drive system 500 or based on a command from an automated process. Third inverter 240_3 is precharged by precharge circuit 330 during time period t2 while inverters 240_1 and 240_2 remain connected to DC bus 310 and continue to receive electrical power from DC bus 310.

As shown in fig. 5D, during a time period t2, the third inverter 240_3 is connected to the precharge circuit 330. Current i _330 flows from precharge circuit 330 to capacitor network 247_ 3. As shown in fig. 5A, the magnitude of the current i _330 fluctuates within the exponentially decaying envelope during the time period t 2. The ripple is due to the rectification performed by the precharge circuit 330. The voltage across the capacitor network 247_3 (shown as 547x in fig. 5B) increases from 0 at the beginning of time period t2 to its threshold voltage V2. After the capacitor network reaches the threshold voltage V2, the time period t2 ends. As shown in fig. 5E, immediately after the second time period t2, the third inverter 240_3 is disconnected from the precharge circuit 330 and connected to the common DC bus 310. The voltage across capacitor network 247_3 becomes the same as the voltage across common DC bus 310.

Thus, third inverter 240_3 is connected to drive system 500 and common DC bus 310 without interfering with the operation of inverters 240_1 and 240_2, and while also minimizing or eliminating inrush currents that may otherwise occur in capacitor network 247_ 3. In the above example, the precharge circuit 330 acts as an auxiliary or supporting precharge circuit that allows the inverter to be swapped or replaced, or allows additional inverters to be added without interfering with the operation of the inverters already powered by the common DC bus 310.

The scenarios discussed above are provided as examples, and other scenarios are possible. For example, any of inverters 240_1 through 240_3 connected to common DC bus 310 may be disconnected from common DC bus 310 without interfering with the operation of the inverters remaining connected to common DC bus 310. For example, after time period t2, all inverters 240_1 through 240_3 are connected to common DC bus 310. Any of the inverters 240_1 through 240_3 may be removed from the common DC bus 310 by opening the respective switching devices 343_1 through 343_ 3. For example, if inverter 240_2 has a fault condition, control system 250 opens switching device 343_2, thereby removing inverter 240_2 from common DC bus 310. Switching device 344_2 remains open such that inverter 240_2 is disconnected from drive system 500. The other inverters 240_1 and 240_3 remain connected to the common DC bus 310 through switching devices 343_1 and 343_ 3. Inverters 240_1 and 240_3 continue to be operable when inverter 240_2 is removed from common DC bus 310 and after inverter 240_2 is removed from common DC bus 310. An example of a process for removing the inverter from the drive system is discussed below with respect to fig. 8.

FIG. 6 is a schematic diagram of another example drive system 600. Drive system 600 is the same as drive system 300 (fig. 3), except that drive system 300 includes precharge circuit 630 instead of precharge circuit 330. The precharge circuit 630 includes an impedance 634 but does not include a rectifying element. Instead, the DC power is provided directly to the input node 631 of the precharge circuit 630. In the example shown in fig. 6, input node 631 is electrically connected to the high side 310a of common DC bus 310. Precharge circuit 630 includes an output node 632 that is electrically connected to inverter 240_1 when switching device 344_1 is closed and/or to inverter 240_2 when switching device 344_2 is closed.

Fig. 7 is a flow diagram of a process 700. Process 700 is an example of a process for replacing an inverter or adding an inverter in an already operating drive system. The process 700 may be used with the systems 100, 200, 300, 400, 500, or 600, although the process 700 is discussed below with respect to the system 400. The process 700 may be performed by the processing module 252 of the control system 250.

Process 700 begins when a run command is received at drive system 400 (705). The run command is a command indicating that the inverter currently offline is to be added to the drive system 400. The run command may be received from an operator via the I/O interface 256. In some embodiments, the run command is generated automatically without operator intervention. The run command may be received at the electronic processing module 252. In the example discussed below, inverter 240_2 is offline and inverter 240_1 is online and connected to common DC bus 310. In this example, process 700 is used to connect inverter 240_2 to common DC bus 310.

After receiving the run command, control system 250 determines the state of the first switch that controls the connection between inverter 240_2 and precharge circuit 330 (715). In this example, the first switch is switching device 344_ 2. To perform (715), control system 250 determines whether switching device 344_2 is open or closed. In some embodiments, control system 250 also determines the state of a second switch that controls the connection between inverter 240_2 and common DC bus 310 to ensure that inverter 240_2 is not electrically connected to common DC bus 310 at initial startup. In this example, the second switch is the switching device 343_2 in this example. If switching device 343_2 is closed, control system 250 opens the switches in switching device 343_ 2. For example, control system 250 may generate command signal 251 that includes information sufficient to open a closed switch in switching device 343_ 2.

If switching device 344_2 is closed, current i _330 flows from precharge circuit 330 to capacitor network 247_2 of inverter 240_2, thereby operating precharge circuit 330 (725). The voltage at capacitor network 247_2 begins to increase. The voltage difference between the common DC bus 310 and the local DC bus 242_2 of the inverter 240_2 is measured by sensor 349_ 2.

Control system 250 analyzes the voltage measured at sensor 349_2 to determine whether capacitor network 247_2 has been sufficiently precharged (530). For example, a pre-charge condition threshold voltage representing a minimum difference between the common DC bus voltage (V _ bus) and the inverter local DC bus voltage may be stored on electronic storage 254. The precharge condition threshold voltage may be the magnitude of the difference between the voltage across common DC bus 310 (V _ bus) and the voltage across local DC bus 242_ 2. The value of this difference is chosen to be a value that is small enough not to cause a rush current or to cause only a relatively small rush current. The threshold may be, for example, zero (0) volts (V), meaning that an individual inverter will satisfy a pre-charge condition if the voltage across the common DC bus 310 is the same as the voltage at its respective local DC bus. Other values may be used for the threshold, and the threshold may be a value other than zero, depending on the application.

If inverter 240_2 has achieved the precharge condition, control system 250 operates switching device 344_2 to disconnect inverter 240_2 from precharge circuit 330 (735). For example, control system 250 may generate command signal 251 and provide command signal 251 to switching device 344_ 2. In this example, command signal 251 may be a voltage signal sufficient to cause a switch in device 344_2 to open. In this example, opening switching device 344_2 disconnects inverter 240_2 from precharge circuit 230.

The control system 250 issues a command to close a second switch, which in this example is switching device 343_2 (740). When switching device 343_2 is closed, inverter 240_2 is electrically connected to common DC bus 310, and inverter 240_2 is on and generates drive signals 204_2 (785). Inverter 240_1 remains connected to DC common bus 310 during process 700. The operation of inverter 240_1 is not affected by process 700.

After (705) through (740) are performed, inverter 240_2 should have been precharged by precharge circuit 330 and electrically connected to common DC bus 310. However, problems may arise with the operation of switching device 344_2 or switching device 343_ 2. Process 700 checks for such problems as described below.

Returning to (715), if switching device 344_2 is not closed based on the (710) determination, control system 250 attempts to close switching device 344_ 2. Control system 250 determines whether switching device 344_2 is closed (755). If switching device 344_2 is closed, process 700 returns to (725). If switching device 344_2 is not closed, control system 250 determines that switching device 344_2 is in a fault condition (760). Control system 250 takes action to repair the fault condition in switchgear 344_2 (765). For example, control system 250 may issue a perceptible alert to an operator indicating that switching device 343_2 is in a fault condition and should be repaired or replaced. If the fault condition is not resolved, process 700 returns to (760). If the fault condition is repaired, process 700 returns to (750) and control system 250 again attempts to close switching device 344_ 2.

The switching device 343_2 is also tested for failure as described below. After attempting to close switching device 343_2 at (740), the control system determines whether switching device 343_2 is closed (770). If switching device 343_2 is not closed, control system 250 determines the fault with switching device 343_2 (775) and control system 250 attempts to repair the fault (780). For example, the control system 250 may alert an operator so that a repair or replacement may be made. If the failure is repaired, process 700 returns to (740). If the fault is not repaired, process 700 returns to (775) until the fault is repaired.

The above example involves connecting inverter 240_2 to common DC bus 310 while inverter 240_1 remains connected to common DC bus 310 and does not interrupt operation of inverter 240_ 1. Process 700 may be applied to connect other inverters to common DC bus 310.

Referring to fig. 8, a flow diagram of a process 800 is shown. Process 800 is an example of a process for shutting down one or more inverters in a drive system. Process 800 is discussed with respect to drive system 400, but may be performed with other drive systems, such as system 200 or system 300. The process 800 may be performed by the control system 250.

A close command is received (805). The close command may be a command from an operator entered at the I/O interface 256. As another example, the shutdown command may be a command that is automatically issued due to, for example, one or more of the N inverters 240 exceeding their safe operating limits. In the example below, inverter 240_1 and inverter 240_2 are initially connected to a common DC bus 310. Inverter 240_2 is off.

Inverter 240_2 is disabled (810). Control system 250 attempts to open switching device 343_2 (815). Disconnecting switching device 343_2 disconnects inverter 240_2 from common DC bus 310. Control system 250 determines whether switching device 343_2 is open (820). If switching device 343_2 is determined to be open, inverter 240_2 is turned off (825).

If switching component 343_2 is not determined to be open at (820), control system 250 determines that switching device 343_2 is in a fault condition (830). Control system 250 then attempts to manually open switching device 343_2 (835). After manually opening switching device 343_2, inverter 240_2 is shut down and considered shut down (825). During process 800, inverter 240_1 remains connected to common DC bus 310 and continues to operate uninterrupted.

The above example is discussed with respect to shutting down inverter 240_ 2. In other examples, different ones of the N inverters 240 are off. In other examples, more than one of the N inverters 240 is shut down at the same time.

Fig. 9 is a flow chart of a process 900. Process 900 is an example of a process for a fault diagnosis process. The process 900 may be performed by the control system 250. Process 900 may be used to perform fault diagnosis on drive system 100, 200, 300, 400, 500, or 600. For purposes of providing an example, process 900 is discussed with respect to drive system 400.

A fault diagnosis command is received (905). The fault diagnosis command may be accepted by the control system 250. For example, an operator of system 300 may request manual troubleshooting via I/O interface 256. As another example, a fault diagnosis command may be automatically generated by the system 300 and provided to the control system 250 when a fault is detected.

The N inverters 240 are evaluated to determine the operating states of the N inverters 240 (910). The N inverters 240 may be evaluated, for example, by analyzing the drive signals 204_1 through 204_ N to determine whether the drive signals 204_1 through 204_ N have characteristics (e.g., amplitude, frequency, and/or phase) within an expected range of connected loads.

If all N inverters 240 are in normal operation (920), process 900 returns to (910) to continue monitoring N inverters 240, or process 900 may end until another fault diagnosis command is received. If one or more of the N inverters 240 are not in normal operation (920), control system 250 attempts to identify a fault or faulty one or more inverters (930). The inverter has a fault condition due to, for example, overheating, overcurrent, overvoltage, and/or component failure. A fault or faulty inverter or inverters can be identified by analyzing the drive signals 204_1 through 204_ N and/or determining whether a drive signal was generated by a particular one of the N inverters 240.

If control system 250 identifies one or more failed inverters, the identified failed inverter or inverters are processed (940). The failed inverter handling includes completing a disconnection process, offline repair or replacement of the failed inverter or inverters, and reconnecting the failed inverter. Process 800 (fig. 8) is initiated in order to disconnect or shutdown the identified faulty inverter or inverters. For example, if inverter 240_1 is the inverter of the identified fault, inverter 240_1 is disabled (910), switching device 343_1 is opened (915), and switching device 343_1 is evaluated for faults (930) through (935), if necessary. After performing process 800, inverter 240_1 is deemed to be off. The failed inverter 240_1 is repaired or replaced while offline. The failed inverter 240_1 is then reconnected using process 700 (fig. 7). One or more inverters that are operating normally (i.e., inverters that are not identified as faulty) continue to operate while the process (940) occurs.

The faulty inverter or inverters are evaluated to determine if they are operational (960). Continuing with the example where the identified faulty inverter is inverter 240_1, control system 250 may receive and analyze information about drive signal 204_1 to determine whether inverter 240_1 is operational.

Returning (930), if a failed inverter or inverters is not identified, control system 250 tests each of the N inverters one by one to find a failed inverter. The untested inverters remain connected to the common DC bus 310 and therefore remain operational (unless in a fault condition). An inverter (970) that may fail is identified. For example, inverter 240_2 may be identified as a possible fault or as a candidate for a failure or fault. The identified potentially faulty inverter (240 _2 in this example) is processed (940). The process (940) is discussed above. After completing the process (940), the potentially faulty inverter (240 _2 in this example) is evaluated to determine its operational status (980). If the potentially failing inverter (240 _2 in this example) is operational, process 700 ends (985). If the potentially failing inverter is not operational at (980), the process returns to 970 and identifies another inverter of the N inverters 240 as a potentially failing inverter. If desired, process 900 may continue to perform (970), (940), and (980) until all N inverters 240 have been processed. After N inverters 240 are operational, process 900 ends.

Other implementations are within the scope of the following claims.

For example, any pre-charge circuit known in the art that receives an AC power input and produces a DC or rectified output may be used as pre-charge circuit 330 (fig. 3). As another example, any pre-charge circuit known in the art that receives a DC electrical input and produces a DC output may be used as pre-charge circuit 630 (fig. 6). Further, the switch assemblies 270_1 to 270_ N and the switch devices 343_1, 343_2, 343_3, 344_1, 344_2, 344_3 discussed above are examples and any other switch network capable of connecting the inverter to the pre-charge circuit or the common DC bus may be used.

Systems 200, 300, and 600 may include a common precharge circuit similar to common precharge circuit 480 shown in fig. 4 and 5C-5E, except for respective precharge circuits 230, 330, 630. In embodiments that include a common precharge circuit, at initial power-on or startup when all N inverters are turned on from an off state, the capacitor network of the local DC bus of each of the N inverters is initially precharged by the common precharge circuit. In these embodiments, the precharge circuits 230, 330, 630 precharge the local DC buses of the individual inverters connected to the common DC bus after the other N inverters have been connected to the common DC bus. Nonetheless, systems 200, 300, and 600 may be implemented without a common precharge circuit and with only respective precharge circuits 230, 330, 630. In these embodiments, the precharge circuits 230, 330, and 630 can precharge the capacitor networks associated with all of the inverters in the systems 200, 300, 600 at startup, and are further configured to precharge the capacitor networks on the local DC bus of additional inverters while some or all of the original inverters remain connected to the common DC bus.

Claims (13)

1. A system, the system comprising:

a pre-charge circuit configured to generate Direct Current (DC) electrical power;

a common DC bus; and

a plurality of inverters, each inverter comprising:

a local DC bus;

a capacitor network connected to the local DC bus;

an electrical network connected to the local DC bus, the electrical network configured to generate an Alternating Current (AC) drive signal; and

a plurality of switching assemblies, each switching assembly associated with one of the inverters and configured to control whether the local DC bus and the capacitor network of the associated inverter are electrically connected to the common DC bus or to the pre-charge circuit.

2. The system of claim 1, wherein the pre-charge circuit is configured to provide DC electrical power to the capacitor network of the local DC bus of at least one other of the plurality of inverters when the local DC bus of at least one of the plurality of inverters is electrically connected to the common DC bus.

3. The system of claim 1, wherein the pre-charge circuit is electrically connected to an AC power source and further comprises at least one electronic component configured to convert AC electrical power to DC electrical power.

4. The system of claim 3, wherein the at least one electronic component configured to convert AC electrical power to DC electrical power is a diode.

5. The system of claim 1, further comprising a converter electrically connected to the AC power source and the common DC bus, and wherein the converter is configured to convert AC electrical power from the AC power source to DC electrical power and provide the DC electrical power to the common DC bus.

6. The system of claim 5, wherein the converter is a front end rectifier and the AC power source comprises a multi-phase high voltage electrical power distribution network.

7. The system of claim 1, wherein the pre-charge circuit is electrically connected to the common DC bus and the pre-charge circuit receives DC electrical power from the common DC bus.

8. The system of claim 1, further comprising a control system configured to control the plurality of switch assemblies.

9. The system of claim 1, wherein the pre-charge circuit is an auxiliary pre-charge circuit, and the system further comprises a common pre-charge circuit electrically connected to the common DC bus, and wherein the common pre-charge circuit is configured to provide a DC pre-charge current to all of the capacitor networks when the capacitor networks are electrically connected to the common DC bus, and the auxiliary pre-charge circuit is configured to pre-charge a capacitor network associated with another inverter when at least some of the other capacitor networks are electrically connected to the common DC bus.

10. A method, the method comprising:

electrically connecting a local DC bus of a first inverter to a common DC bus, wherein the first inverter is associated with a first switching assembly;

operating a second switching assembly associated with a second inverter to electrically connect a local DC bus of the second inverter to a pre-charge circuit when the local DC bus of the first inverter is electrically connected to the common DC bus and when the local DC bus of the first inverter receives DC electrical power from the common DC bus;

comparing a voltage of a capacitor network electrically connected to the local DC bus of the second inverter to a threshold voltage when the local DC bus of the first inverter is electrically connected to the common DC bus and when the local DC bus of the first inverter receives DC electrical power from the common DC bus; and

determining whether to disconnect the local DC bus of the second inverter from the pre-charge circuit and whether to connect the local DC bus of the second inverter to the common DC bus based on the comparison, wherein

The first switching component is configured to connect the local DC bus of the first inverter to the common DC bus or the pre-charge circuit, and the second switching component is configured to connect the local DC bus of the second inverter to the common DC bus or the pre-charge circuit.

11. The method of claim 10, wherein determining whether to disconnect the local DC bus of the second inverter from the pre-charge circuit and whether to connect the local DC bus of the second inverter to the common DC bus based on the comparison comprises disconnecting the first inverter from the pre-charge circuit if a measured voltage of the local DC bus of the second inverter is equal to or greater than the threshold voltage.

12. The method of claim 10, further comprising precharging a capacitor network of the first inverter with a common precharge circuit electrically connected to the common DC bus prior to operating the second switching component.

13. A system, the system comprising:

a pre-charge circuit configured to generate Direct Current (DC) electrical power;

a common DC bus;

a plurality of inverters, each inverter comprising: a local DC bus, a capacitor network electrically connected to the local DC bus, and an electrical network electrically connected to the local DC bus, the electrical network configured to generate an Alternating Current (AC) drive signal, and wherein the capacitor network of each inverter is configured to be electrically connected to the common DC bus or the pre-charge circuit.

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